1. Field of the Invention
The present invention relates to a feeding device that feeds recording media and an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile provided with the feeding device.
2. Description of the Related Art
A feeding device in an image forming apparatus can store therein recording paper in a stacking manner and is provided with a single- or multiple-stage paper feed tray (or paper cassette) that is detachable with respect to the main body of the image forming apparatus. The paper feed tray is attached to or detached from the image forming apparatus main body typically via an opening provided on one surface of the image forming apparatus.
The image forming apparatus of this type transmits information of the size of paper stored in the paper feed tray to a controller in the image forming apparatus main body so that the copying or printing is correctly performed. As a mechanism to simply transmit the paper size information to the controller, known are some mechanisms in which a rotary dial is provided on a front panel of a paper feed tray, and a user operates the dial to encode and transmit the paper size to the controller (Japanese Laid-open Patent Publication No. 6-100198, Japanese Laid-open Patent Publication No. 11-59920, Japanese Laid-open Patent Publication No. 2009-73664, and Japanese Laid-open Patent Publication No. 9-290929).
As a mechanism of this type, Japanese Laid-open Patent Publication No. 6-100198 discloses a structure in which pressing components in a projecting shape as an encoder are attached on a reverse face of a disc shaped indicator plate rotatably supported on a paper cassette, and when the paper cassette is attached to the main body, a plurality of switches provided on the main body are selectively pressed by the pressing components, thereby detecting the paper size. Japanese Laid-open Patent Publication No. 11-59920 discloses a similar structure.
Furthermore, Japanese Laid-open Patent Publication No. 2009-73664 discloses a structure in which a columnar dial is rotatably disposed on a paper feed tray and a plurality of cams are provided on an outer circumferential surface of the dial at different positions in height and in the circumferential direction, and the attaching operation of the paper feed tray makes the cams selectively press size detecting switches provided on the main body side to detect the paper size. Moreover, Japanese Laid-open Patent Publication No. 9-290929 discloses a structure in which a plurality of peaks are projected in the radial direction of a size indicator plate and rotating the size indicator plate makes the peaks contact switches to activate sensors.
The general-purpose detecting sensors are structured with switches lined up in a row, and thus in the mechanism in which the switches are disposed facing the reverse face of the disc shaped indicator plate as in Japanese Laid-open Patent Publication No. 6-100198 and Japanese Laid-open Patent Publication No. 11-59920, it is unavoidable that the diameter of the indicator plate becomes large. Consequently, the installation space for the indicator plate is restricted, and the flexibility of design is lowered. While Japanese Laid-open Patent Publication No. 6-100198 discloses a usage example of sensors in which switches are lined in two rows, such sensors are not generic and thus lead to a cost increase.
Furthermore, the structure in Japanese Laid-open Patent Publication No. 2009-73664 needs to provide the same number of rows of cams as the number of switches for the sensors on the outer circumferential surface of the columnar dial in the axial direction, and thus the size of the dial in the axial direction tends to be large. The structure in Japanese Laid-open Patent Publication No. 9-290929 requires, in addition to the space for the size indicator plate, the space for the rotational locus of the peaks when rotating the size indicator plate, and thus the installation space is similarly restricted.
Therefore, there is a need to achieve the downsizing of and lowering the cost of a mechanism that encodes size information of a recording medium.